This invention relates to compatible blends of epoxy resins and epoxidized polydiene polymers. More specifically, the invention relates to blends of epoxy resins and epoxidized polydienes which are compatibilized and cured with anhydride curing agents.
Epoxy resins such as glycidyl ethers prepared by the reaction of epichlorohydrin with a compound containing at least one hydroxyl group carried out under alkaline reaction conditions are known to be useful in adhesives, and particularly in structural adhesives. Such epoxy resins are described in U.S. Pat. No. 5,169,910. Structural adhesives are bonding agents used to form permanent load bearing joints between adherands and generally should have the characteristics of high strength, good adhesion, and environmental resistance. Structural adhesives containing such epoxy resins have the disadvantage that they tend to be inflexible and have low impact resistance.
Low viscosity epoxidized polydiene polymers are also known to be useful in adhesives. Such polymers are described in U.S. Pat. Nos. 5,224,464 and 5,247,026. These polymers have a relatively high degree of flexibility and also a relatively high impact resistance.
It would appear to be advantageous to blend the epoxy resins with the polydienes to obtain blends which have the desirable characteristics of both of the polymers, i.e., high strength along with good flexibility and impact resistance. However, it has been found that epoxy resins of this type are incompatible with polydienes. This is discussed in more detail in the examples below. Thus it is clear that it would be advantageous to be able to produce a compatible blend of an epoxy resin and an epoxidized polydiene. The present invention provides a blend of these two polymers which is compatibilized and cured by incorporating the same material, an anhydride curing agent.